As the number of electronic resources proliferate, the demand for applications to facilitate communications between such resources will also increase. Such applications can include electronic commerce but also secure sharing of data through encrypted or digitally signed electronic mail (e-mail) or secure access to resources through file sharing or remote computer log-on. All of these uses of cryptography require the authentication of users and other data prior to performance of a particular action. That is, it requires a level of trust to be established prior to performance of the transaction.
Specifically, in this networking age, a person is normally authenticated not by personal appearance but rather by use of a cryptographic key. In order for a particular key to correctly represent some person (or other entity), the party accepting the key would need to establish that the particular key is controlled by that person or entity. This process is normally referred to as “key verification”. Current key verification techniques are either inadequate and therefore prone to error or abuse or they are so unusual and technical that an average human user might shy away from that activity.
For instance, one key verification technique (referred to as “directory verification” and first described in an Institute of Electronic and Electrical Engineering (IEEE) Transaction on Information Theory publication entitled “New Directions in Cryptography” by Whitfield Diffie and Martin Hellman (November 1976, pp. 644–654)) involves the publication and global distribution of a printed reference that includes the name, address and assigned public key for each user. The reference is published by a trusted source and distributed in a secure manner. One of many disadvantages of the directory verification technique is that it is costly to implement. Namely, this technique would incur additional costs for publication of the reference, secure distribution of the reference, and for each listed keyholder in the directory, the proof to the trusted source that the user is the true owner of the public key prior to publication. Another disadvantage is that the names of the users may be unique in a small group, but such uniqueness diminishes for larger groups. Hence, as the size of the group gradually expands, name collisions are almost certain to occur. When names collide, any party relying on the directory's results will not always be able to locate the correct directory entry for a desired person or other entity with certainty and therefore be not always able to locate that person's or entity's public key.
Other key verification techniques include the exchange of a digital certificate in accordance with, for example, Request For Comment (RFC-2459) entitled “Internet X.509 Public Key Infrastructure” (January 1999). However, the X.509 mechanism also suffers from the requirement of a central trusted source and increased costs for establishing such a certificate mechanism. It also suffers from name collision with the added disadvantage that when names collide, the user of a certificate may not be aware of the collision because he or she sees only the one directory line item contained within the certificate at hand and not the neighboring region of the directory.
Yet another key verification technique has been established by the application program referred to as “Pretty Good Privacy” (PGP). The idea of PGP key verification is to bind a public key of an owner to his or her global name, such as an e-mail address, for example, without the cost of a central trusted source. PGP allows every user to generate his or her own keys and certificates. For key verification purposes, PGP computes a fingerprint of the key to be verified, in the form of a cryptographic hash result of that key. This hash result is computed independently by the keyholder's copy of PGP and the relying party's copy of PGP. These cryptographic hash results, displayed either in the form of a long hexadecimal number or a sequence of English words, are then compared by having one party read the value to the other. If the values match, then the key in question is verified.
The PGP key verification technique has the disadvantage that the technique of visually or audibly comparing a number of hexadecimal character values or a string of meaningless words is quite time consuming and strange for the user who wants to achieve appropriate authentication levels. Because of that workload, some users skip the verification step entirely.